This invention relates to ceramic broadband radomes, and in particular to a monolithic silicon nitride radome.
In various types of aircraft and missiles carrying radar equipment, an antenna is mounted in the nose of the craft and is covered with a suitable aerodynamic surface or radome. The radome must be constructed of material which is strong enough t withstand the aerodynamic forces to which it may be submitted, yet must be relatively distortion-free and highly transparent to radar energy.
Ceramic radomes appear to offer the best combination of low weight, high temperature strength, electromagnetic transmissibility. and thermal insulation, particularly for missiles encountering boundary layer temperatures over about 400.degree. C. Ceramic materials with dielectric properties suitable for use as solid wall radomes are generally limited to silicon nitride, alumina. silica, mullite and beryllia. None of these materials, with the required dielectric constant of less than 10.0 and loss tangent of less than 0.01, has heretofore met the criteria of high transmission efficiency, rain erosion, and thermal stress resistance which are required of a radome for Protection of antennas operating over a broad frequency range, when fabricated as a monolithic wall structure.
Low density silicon nitride appears attractive as a monolithic radome material. However, such low density material lacks the mechanical properties necessary for attaching the rear portion of the radome to a desired structure. Perry, U.S. Pat. No. 4,520,364, discloses a composite transition section interposed between a monolithic ceramic radome and a metal airframe. The transition section is adhesively bonded to the radome shell and bolted to the metal airframe. What is desired, however is a monolithic ceramic radome which has the desired electrical properties together with mechanical Properties for adequate load transfer for attachment purposes.
Accordingly, it is an object of the present invention to provide a monolithic silicon nitride radome structure.
Another object of the present invention is to provide a method for fabricating a monolithic silicon nitride radome.
Other objects and advantages of the present invention will become apparent to those skilled in the art from consideration of the following description of the invention.